Starch is made up of a mixture of amylose (15-30% w/w) and amylopectin (70-85% w/w). The amylose part consists of linear chains of alpha-1,4-linked glucose units having a molecular weight (MW) ranging from about 60,000 to about 800,000. The amylopectin part is a branched polymer containing alpha-1,6 branch points every 24-30 glucose units; its MW may be as high as 100 million.
A number of enzymes are involved in the degradation of starch, including, for example, alpha-amylases, beta-amylases, amyloglucosidases, pullulanases, isoamylases, alpha-glucosidases, cyclodextrin glycosyltransferases and the like.
As a class, alpha-glucosidases (EC 3.2.1.20) are capable of catalyzing the liberation of glucose from non-reducing ends of alpha-glucosides, alpha-linked oligosaccharides, and/or alpha-glucans. These enzymes show diverse substrate specificities, however; some prefer alpha-linked di-, oligo-, and/or polyglucans, while others preferentially hydrolyze heterogeneous substrates such as aryl glucosides and sucrose. See, Chiba, S. (1988) Alpha-Glucosidases, pp. 104-105. The Amylase Research Society of Japan (ed.), Handbook of Amylases and Related Enzymes. Pergamon Press, Oxford, United Kingdom.
Alpha-glucosidase is a retaining glycosyl hydrolase (GH), capable of catalyzing transglycosylation. See, Chiba, S. (1997) Biosci. Biotechnol. Biochem. 61:1233-1239. For example, buckwheat alpha-glucosidase hydrolyzes soluble starch to produce kojibiose (2-O-alpha-glucosyl-glucose), nigerose (3-O-alpha-glucosyl-glucose), maltose, and/or isomaltose. See, Chiba, S. (1988), supra. Alpha-glucosidases from Bacillus stearothermophilus and brewer's yeast, on the other hand, hydrolyzes starch to produce oligosaccharides consisting of alpha-1,3, alpha-1,4, and/or alpha-1,6 linkages. See, Mala S., et al., (1999) Carbohydr. Res. 322:209-218.
Alpha-glucosidases are often used in conjunction with other starch-degrading enzymes, including, for example, alpha-amylase, glucoamylases, and the like, to drive more complete hydrolysis of starchy substrates into soluble fermentable sugars, which are useful for various downstream industrial applications. Depending on the industrial applications, alpha glucosidases or other enzymes suitable for these industrial processes can be diverse. There is as such always a need in the art for alternative alpha-glucosidases with improved or different properties such as pH optimum, temperature optimum, substrate specificities, and/or thermostability.
It is an object of the present disclosure to provide certain polypeptides having alpha-glucosidase activity, polynucleotides encoding the polypeptides, nucleic acid constructs that can be used to produce such polypeptides, compositions comprising thereof, as well as methods of making and using such polypeptides.